Acceptor Pair‐Bound Exciton Complexes in Semiconductors

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Abstract
The evolution of the principal bound exciton (PBE) line, for bound exciton‐neutral acceptor(s) complex(es), between low (≦ 1016 cm−3) and high (>1017cm−3 acceptor concentrations in semiconductors, is studied. Photoluminescence experiments are performed in ZnTe, for the five wellknown acceptors Li, Na, Ag, Cu, Au and for several doping levels. High concentrations provide an asymmetric broadening with undulations and a shift to lower energies of the PBE line. Semiempirical calculations are made for the neutral acceptor pair‐bound exciton complex. In ZnTe good agreement is obtained with experiment. The calculations demonstrate that the empirical relation ΔE(R) = E0, exp (−R/R0)3 is a good and simple analytical approximation of the bound exciton localization energy shift, when the exciton is bound on a neutral acceptor pair, with a pair separation R. These calculations permit to evaluate the energy shift of the PBE line maximum for acceptors in highly doped semiconductors.